Chapter: Linear Integrated Circuits : Basics of Operational Amplifiers

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Slew Rate

Slew rate is the maximum rate of change of output voltage with respect to time. Specified in V/μs.

Slew Rate

 

Slew rate is the maximum rate of change of output voltage with respect to time. Specified in V/μs.

 

Reason for Slew rate:

There is usually a capacitor within 0, outside an op-amp oscillation. It is this capacitor which prevents the o/p voltage from fast changing input. The rate at which the volt across the capacitor increases is given by

dVc/dt = I/C --------(1)

I -> Maximum amount furnished by the op-amp to capacitor C.

Op-amp should have the either a higher current or small compensating capacitors.

For 741 IC, the maximum internal capacitor charging current is limited to about 15μA. So the slew

rate of 741 IC is

SR = dVc/dt |max = Imax/C

For a sine wave input, the effect of slew rate can be calculated as consider volt follower. The input is large amp, high frequency sine wave.

If Vs =Vm Sinwt then output V0 = Vm sinwt .

The rate of change of output is given by dV0/dt=Vm w coswt.


The max rate of change of output across when coswt =1

(i.e)  SR =dV0/dt |max = wVm.

SR = 2 fVm V/s = 2fVm  v/ms.

Thus the maximum frequency fmax at which undistorted output volt of peak value Vm is given by fmax (Hz) = Slew rate/6.28 * Vm called the full power response. It is maximum frequency of a large amplitude sine wave with which op-amp can have without distortion.

 

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